How to pull specific data from solution set?

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Tom Keaton 2018-10-31

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https://ww2.mathworks.cn/matlabcentral/answers/427268-how-to-pull-specific-data-from-solution-set

评论： Tom Keaton 2018-11-1

Hello, I am using this ODE solver and I am trying to figure out how I can reference the velocity components of the matrix of solutions. I think I would know how to pull the position components given the assigned variables below because the matrix "W" contains them, but how may I be able to define a velocity matrix of solutions? For context, I am solving the Lorentz force equations. The x, y and z and vx, vy and vz components are predefined and can be completely random. The "vparts" and "sparts" are the velocity and position components of arrays.

Main Script:

[X,Y,Z] = meshgrid(-0.5:.01:0.5,-0.5:.01:0.5,-0.5:.01:0.5);
[Bx, By, Bz] = B_test();
Bfieldx = arrayfun(Bx,X,Y,Z);
Bfieldy = arrayfun(By,X,Y,Z);
Bfieldz = arrayfun(Bz,X,Y,Z);
icv = [x; y; z; vx; vy; vz];
%Time Span (sec)
tspan = [0 tstep];
[T,W] = ode15s(@bdipuniodefun, tspan, icv);
[rownum,colnum] = size(W);
plot3(W(:,1), W(:,2), W(:,3), '-r', 'LineWidth',2,'color',[randi(0:1) randi(0:1) randi(0:1)])
xlabel 'x';
ylabel 'y';
zlabel 'z';
grid on
      
%Redfine the velocity and position components to reference on next if-loop run
vparts(1) = vx;
vparts(2) = vy;
vparts(3) = vz;
sparts(1) = W(rownum,1);
sparts(2) = W(rownum,2);
sparts(3) = W(rownum,3);

B_Test:

function [Bx, By, Bz] = B_test()
syms x y z
mu_0_red = 10E-7;
m = [0,0,1.28];
r = [x, y, z];
B = mu_0_red *(((dot(m,r)*r*3)/norm(r)^5) - m/norm(r)^3);
Bx = matlabFunction(B(1));
By = matlabFunction(B(2));
Bz = matlabFunction(B(3));

bdipolefun:

function bdip = bdipuniodefun(t,s)
%Using SI units
q = 1.60217662E-19;
m_e = 9.11E-31;
[Bx, By, Bz] = B_test();
bdip = [s(4); s(5); s(6); (q/m_e)*(s(5)*Bz(s(1),s(2),s(3)) - s(6)*By(s(1),s(2),s(3))); (q/m_e)*(s(6)*Bx(s(1),s(2),s(3)) - s(4)*Bz(s(1),s(2),s(3))); (q/m_e)*(s(4)*By(s(1),s(2),s(3)) - s(5)*Bx(s(1),s(2),s(3)))];